All the basic wrist stretches (e.g. flexion, extension) are good, and you can do ulnar and radial deviation as well. On the ulnar deviation, you can grab your thumb inside your fist to get more of a stretch. That one sometimes does wonders for people's wrist pain.
You may also have some tightness higher up in the forearms. If you can get that loosened up and smoothed out, you may get some relief in the wrists as well. I would suggest a good manual therapist for that, although you can try self massage with the thumb, trying to find any tight spots and work them out.
You can try contrast on on the wrists too - alternating cold and hot water plunges (you can fill a bucket or plastic trash can with ice water and another with hot water - one hand/wrist in each for a couple minutes, then switch. Finish with hot).